This section provides background information related to the present disclosure which is not necessarily prior art.
Inverter drives, also known as variable frequency/speed drives or simply drives, are electronic devices designed to provide a controllable AC current to a motor driving a load, so as to vary the motor speed.
In cases where the torque of the load pulsates, for example if the load is a reciprocating pump or compressor, the fluctuations in the torque are transmitted back to the inverter drive, assuming the motor is operated at a constant speed. These fluctuations manifest themselves as corresponding fluctuations in the electrical power input and supply voltage of the inverter drive. This may cause irritating flicker of electrical lighting in the vicinity of the inverter drive.
There exists a range of flicker frequencies, between about 100 and 1,500 cycles per minute, to which the eye is particularly sensitive. In such cases, the restrictions placed on equipment capable of generating such flicker frequencies can be quite severe, and it can be difficult to deploy certain designs of machine which tend to cause torque fluctuations in this range. For example, there are technical standards such as IEC 61000-3-3 and IEC 61000-3-11 that place limits on the fluctuation of the current drawn by electrical equipment. If any equipment exceeds these limits then it may not be possible to place the equipment on certain markets. Therefore, when using an inverter drive operating on a pulsating load, it is often desirable to eliminate lighting flicker whenever possible.
The problem of lighting flicker can be reduced by a variety of well-known techniques such as through use of a mechanical flywheel, or through multiple cylinders in the case of a reciprocating pump. However, these methods all bear associated costs and it would be advantageous if such costs could be minimised or eliminated entirely.
The present disclosure seeks to provide an improved method of addressing the problem of lighting flicker, as encountered when an inverter drive operates on a pulsating load.